The other factor is that MLB scheduled a lot of early games within the home division. The NL Central has got to be the weakest division so far. The Cubs got to beat up on Cincinnati and St. Louis, both of whom have had weak pitching, while the Cardinals team hitting has slumped badly. They also play Houston and the Pirates, both of whom have losing records. Once the Cubbies got out of their division, they started losing lots of games, (despite the 3-game sweep over the Nationals.)
